In 2000, Stuart Manley, a bookseller from Northumberland, England, was rummaging through boxes of materials that had been shipped to his store. There was nothing remarkable in the loot except for a quirky poster with an image of the British Crown and the words “Keep Calm and Carry On.”

Manley had never heard the phrase before, but found it sufficiently entertaining to display it on the walls of his store, Barter Books in Alnwick. He later learned that the poster came from a World War II propaganda campaign designed by Winston Churchill’s war cabinet in 1939 to bolster public spirits while families were being separated, with men going off to war and children being sent to safer locations in the countryside. A million copies were printed but never distributed.

Some local residents took notice of the poster on Manley’s wall and asked for copies. That led to a small story in a British magazine in 2005. Then, as Manley once put it, “all hell broke loose.” The poster became a timeless icon of British resilience and the capacity to bounce back with a stiff upper lip and a good cup of tea.

But the lesson of “Keep Calm and Carry On” isn’t that inspiring slogans can really alter the public mood in times of pain. Rather, the story of Manley’s poster reminds us that the desire to persevere — whether against an existential threat, a lone criminal, or something in between — isn’t created by a slogan. “Keep Calm and Carry On” never guided anyone’s response to World War II. The posters weren’t displayed. And yet the British kept calm and carried on.

There has been a lot of focus on resiliency in Boston these last few days, but less on what it actually means. True resilience is a function of competence, not psychology, and the ability to learn from the past.

Years of planning went into the response to Monday’s Boston Marathon bombings, bolstering the city’s capacity to bounce back.

Immediately after the bombings, runners who could see the finish line were diverted to Commonwealth Avenue, sparing Boylston Street from more confused crowds and greater panic. That quick move helped to preserve a massive crime scene; otherwise, explosive materials and other crucial evidence could have been stuck in a runner’s shoe. Then authorities immediately put out a request for home video or any other source of clues.

Those actions by authorities were the product of a constant process of learning from horrors in the past. The lessons learned from the terrorist attacks on 9/11 prompted the quick reactions of first responders in Boston. The skills that soldiers mastered in the wars in Iraq and Afghanistan created competencies that saved lives, and limbs, at the bomb site. The plea for public participation came from a government that has learned that an insular national security apparatus is limited in its capacities.

A resilient society is one that will absorb what it can from this week, and emerge wiser, if still wounded. So many Bostonians have lost so much. And in their honor we should not simply wish for a return to the relative peace of April 14. We should embrace the lessons of this week, study them, regroup, and adapt, in order to create a new baseline that then becomes the starting point for whatever might, one day again, happen to us. And that whole process will repeat itself, if it must.

Resiliency is not a sprint. It is a marathon.

Juliette Kayyem is a columnist for The Boston Globe. She is former assistant secretary of homeland security and security adviser to Gov. Deval Patrick of Massachusetts.